Activity 1. The Food Journey
How does the food change in consistency and form?
Answer: In the digestive system, food undergoes a systematic transformation in consistency and form as it progresses through specific organs. Mastication in the oral cavity initiates the process, breaking down solid food into smaller pieces through chewing and saliva enzymes. Swallowing in the esophagus shapes the mixture into a cohesive bolus. In the stomach, chyme forms, featuring a more liquid consistency due to mechanical churning and protein digestion. The small intestine refines the mixture to a watery state through bile and pancreatic enzymes, breaking down proteins, fats, and carbohydrates. Nutrient absorption in the small intestine alters consistency, leaving a watery residue. In the large intestine, water reabsorption thickens the material into feces, resulting in a dual transformation of consistency and form. Fecal storage in the rectum precedes elimination during a bowel movement, concluding the digestive process and rendering nutrients accessible for absorption and utilization by the body.
How could the body absorb the nutrients from the foods we eat?
Answer: The body absorbs nutrients from the foods we eat primarily in the small intestine through various mechanisms. Monosaccharides such as glucose, fructose, and galactose from carbohydrates are absorbed through facilitated diffusion or active transport. Amino acids from proteins are absorbed via active transport processes in the duodenum and jejunum. Lipids, including triglycerides broken down into monoglycerides and fatty acids, are absorbed through simple diffusion after being emulsified by bile salts into micelles. These micelles transport lipids, fat-soluble vitamins, and cholesterol to absorptive cells, where they are reassembled into chylomicrons. Chylomicrons, too large for blood capillaries, enter the bloodstream through lymphatic vessels. Electrolytes like sodium, bicarbonate, chloride, iodide, and nitrate ions are absorbed actively, while water-soluble vitamins are absorbed via simple diffusion. Vitamin B12, in conjunction with intrinsic factor, is actively transported in the ileum. The absorption of water in the small intestine occurs through osmosis, facilitated by the absorption of electrolytes, monosaccharides, and amino acids, maintaining an osmotic balance with the blood. Overall, about 90% of nutrient absorption takes place in the small intestine, with the remaining 10% occurring in the stomach and large intestine.
References:
Tortora, G. J., & Derrickson, B. H. (2020). Principles of Anatomy and Physiology (16th ed.). John Wiley & Sons, Inc.